I seem to have an issue with
Host.Local.CloseApplication(webElement.Element, delay) method
similar problem with Local.CloseApplication(webElement.Element)
For firefox, most of the time, it cannot close the application.
For ie, it doesn't happen as often as firefox.
For Chrome, so far I haven't encounter this issue.

I am using 5.4. Firefox sometimes just leave the page not closed. sometimes it will displayed a page called "Well, this is embarrassing." See attached screenshot.

I have a session with a support from Ranorex. He is aware of the issue.
He suggests that in order to avoid this kind of issue, use the top level of the element( DOM ) to close the browser. It is basically more reliable.